Type 2 diabetes is the most common chronic disease in the US, affecting 8% of the population. Currently, diabetes is usually diagnosed after a mean delay of 7 years, often after the development of complications. The DPP is designed to determine whether active interventions (intensive life-style or metformin) can prevent or delay the development of non-insulin dependent diabetes mellitus (NIDDM) in individuals who are at high risk by virtue of having Impaired Glucose Tolerance (IGT). Secondary goals include reduction of macrovascular disease and risk factors that accompany IGT and NIDDM. Recruitment began in 1996 and ended in mid-1999, with more than 3,800 recruited subjects. Subjects will be followed for a mean of 4.5 years. The MGH investigators screened more than 8,000 potential volunters at work sites, health fairs, etc and subsequently performed 1,850 OGTT's (Step 2 recruitment) at the MGH Diabetes Center and GCRC they randomized 156 subjects as of June, 1999. The protocol and manual of operations have been implemented.